Fats and oils are a major constituent of cosmetics, pharmaceuticals and foods, in particular pet foods. For the two former, fats and oils contribute to their texture, odor and/or flavor as well as proper activities of the active ingredients contained therein. In the latter, fats and oils contribute to their texture, odor and/or flavor, nutritional value, texture and palatability.
However, lipids are highly susceptible to oxidation during processing or storage, which can lead to rancidity and/or reduce the nutritional value of the product that is finally used. In particular, this results in a food, such as a pet food, being unpalatable, and nutritionally unsatisfying for the subject, such as the pet.
As a consequence, antioxidants are commonly added to fat-containing compositions, such as cosmetics, pharmaceuticals or foods, such as pet foods, to delay the unavoidable fat oxidation process and to extend the shelf life of the fat-containing composition, for example the food product, such as the pet food product.
In order to evaluate the efficacy of antioxidants in fat-containing compositions, several indicators are used such as the period of protection, i.e. the period of time before oxidation of fat starts, or the quantification of primary fat-oxidation products, such as the peroxide value (PV) or secondary fat-oxidation products, such as the hexanal value (HV).
Synthetic antioxidants are widely used to protect oils and fats in the cosmetic, pharmaceutical and food/pet food industries. Due to the possible adverse effects of synthetic preservatives on health, the consumer's demand for natural antioxidants has tremendously increased in the past decades. Various vegetable extracts have been investigated and hundreds of molecules with different chemical structures have been identified as effective natural antioxidants (Brewer, 2011; Pokorny et al., 2001).
The patent application JP19880240514 mentions an agent containing (a) an extract of green tea leaves and (b) tocopherols and/or extract of rosemary, optionally with (c) gallic acid. However, this patent application is silent about the amounts and/or ratios of these compounds. As well known by the skilled person, green tea leaves mainly comprise polyphenols (catechins, epicatechins etc.) but only contain traces of quercetin. In a review, Namal Senanayake (2013) reports an amount of 25 to 35% of polyphenols by dry weight of green tea leaves, predominantly catechins. The publication “Effect of dietary rosemary and α-tocopherols acetate on the oxidative stability of raw and cooked pork following oxidized linseed oil administration”, L. Haak et al., Meat Science 78 (2008) 239-247, studies the effect on the oxidative stability of raw and cooked pork of a 2% dietary administration to pigs of oxidized linseed oil either or not in combination with antioxidants, containing for example α-tocopheryl acetate and/or rosemary extract and/or gallic acid. However, these compounds did not protect the feed against oxidation as they were encapsulated so as to be released only during digestion of pigs. Moreover, a significant lipid pro-oxidant effect of the combination of rosemary extract and gallic acid was observed.
Tocopherols are currently one of the most commercialized natural antioxidants. They exist in most of vegetable oils and have been extensively studied. Tocopherols are widely used in the field of cosmetic, pharmaceutical and food/pet food industries, in particular because these natural antioxidants do not negatively impact the essential functional properties of the products to be obtained (for example, palatability of pet foods).
However, a major issue to the use of tocopherols lies in a relatively short period of protection, the fat-oxidation in a fat-containing composition being frequently less delayed over time than when using other antioxidants, such as synthetic antioxidants.
Furthermore, high peroxide value and hexanal value have been observed when using tocopherols as the sole antioxidant in a fat-containing composition.
Moreover, it has been found that a high amount of tocopherols is lost when added to a fat-containing composition further subjected to a physical and/or thermal treatment, such as during extrusion.
It is recognized that there is a need for an antioxidant combination of natural antioxidants, said combination being useful for enhancing the antioxidant effect of tocopherols in a fat-containing composition.
An object of the invention is thus to provide a combination of natural antioxidants that significantly enhances the antioxidant effect of tocopherols in a fat-containing composition.
Another object of the invention is to provide a combination of natural antioxidants that can be used for significantly delaying fat-oxidation over time in a fat-containing composition and/or for decreasing the loss of tocopherols under a physical and/or thermal treatment of a fat-containing composition.
Another object of the invention is to provide a combination of natural antioxidants having the ability to at least preserve the palatability compared to a product that does not contain a combination of natural antioxidants of the invention.